Method of taking up wear of a grinding wheel on a machine for grinding sheets of glass, and grinding machine implementing such a method

ABSTRACT

A method of taking up wear of a grinding wheel on a machine for grinding sheets of glass, whereby the position of an abrasive surface of the grinding wheel, initially set to an ideal work position such as to obtain a sheet of a given size, is adjusted, following wear of the grinding wheel, by moving the abrasive surface towards a reference surface on the machine, positioned facing and at a predetermined distance from the abrasive surface when the abrasive surface is in the ideal work position; determining the instant of contact between the abrasive surface and the reference surface; arresting the grinding wheel at the instant of contact; and moving the abrasive surface away from the reference surface to an adjustment distance at least equal to the predetermined distance.

[0001] The present invention relates to a machine for grinding sheets ofglass.

BACKGROUND OF THE INVENTION

[0002] To grind outer peripheral portions of a sheet of glass, grindingmachines are used, which comprise, for each side of the work sheet, anumber of side by side grinding heads, each comprising a poweredgrinding wheel set to a respective zero position to remove a respectivequantity of material to form beveled sheets or sheets to a given size orshape.

[0003] To obtain sheets all of the same size and/or shape, all thewheels must be supervised constantly and the initial zero positionsadjusted to take into account inevitable wear of the wheels. For whichpurpose, each wheel is normally fitted to a respective slide in turnfitted to the machine frame, and which is activated by a supervisor who,on detecting any deviation in size, shape and/or surface finish of thesheet coming off the machine, adjusts the wheels until the sheets comingoff the machine are restored to the desired characteristics.

[0004] Though widely used, the above method of checking and adjustingthe wheels fails to provide for obtaining sheets all of the same shape,size and surface finish. The reason for this substantially lies in thezero position adjustment depending on the skill and experience of thesupervisor, who, knowing the expected working life of the wheel undernormal working conditions, and by constantly checking thecharacteristics of the finished sheets, manually adjusts the position ofone or more wheels accordingly. When the adjustment is made, however,there is no guarantee that each wheel is actually set to the ideal workposition, even if the sheets coming off the machine are, at leastinitially, within the given tolerance range, so that one or more wheelssubjected to greater stress may undergo sudden, rapid wear, while othersare subjected to less severe stress than expected.

[0005] Whichever the case, adjustment as described above is aparticularly time-consuming job, which is directly proportional to thenumber of wheels being supervised.

SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide a wheel weartake-up method designed to solve the aforementioned problems in astraightforward, low-cost manner.

[0007] According to the present invention, there is provided a method oftaking up wear of a grinding wheel on a machine for grinding sheets ofglass; the method comprising the steps of setting an abrasive surface ofthe grinding wheel to an ideal work position, such as to obtain a sheetof desired characteristics; and adjusting the position of the grindingwheel to restore said abrasive surface to said ideal work positionfollowing wear of the grinding wheel; characterized in that adjustmentof the position of the grinding wheel comprises the steps of moving saidabrasive surface towards reference means on said machine, positionedfacing and a predetermined distance from said abrasive surface when theabrasive surface is in said ideal work position; determining the instantof interference between said abrasive surface and said reference means;arresting said grinding wheel at said instant of interference; andmoving said abrasive surface away from said reference means to anadjustment distance at least equal to said predetermined distance.

[0008] The present invention also relates to a machine for grindingsheets of glass.

[0009] According to the present invention, there is provided a machinefor working sheets of glass, comprising a supporting frame; a grindingwheel defined by an abrasive surface; actuating means for setting andmaintaining said abrasive surface in an ideal work position such as toobtain a sheet of desired characteristics; and adjusting means foradjusting the position of the grinding wheel with respect to saidsupporting frame, and restoring said abrasive surface to said ideal workposition following wear of the grinding wheel; characterized in thatsaid adjusting means comprise reference means fitted to said supportingframe and facing and a predetermined distance from said abrasive surfacewhen the abrasive surface is in said ideal work position; firstactuating means for moving said abrasive surface towards said referencemeans; detecting means for determining the instant of interferencebetween said abrasive surface and said reference means; stop means forarresting said grinding wheel at the instant of interference; and secondactuating means for moving said abrasive surface away from saidreference means and to an adjustment distance at least equal to saidpredetermined distance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A non-limiting embodiment of the invention will be described byway of example with reference to the accompanying drawings, in which:

[0011]FIG. 1 shows a section of a preferred embodiment of a unit fortaking up wear of a grinding wheel on a machine (shown partly) forgrinding sheets of glass;

[0012]FIG. 2 shows a larger-scale section of a detail in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0013] Number 1 in FIG. 1 indicates as a whole a machine (shown partly)for grinding a sheet 2 of glass having a lateral surface 3 for grindingand placed horizontally on a known supporting device 4 of machine 1.

[0014] Machine 1 comprises a frame 5; and a number of adjustablegrinding heads 6, only one of which is shown in FIG. 1. Each head 6comprises a grinding wheel 7, which is housed inside a sealed chamber 8containing cutting fluid, is rotated about a respective axis 9—in thiscase, a horizontal axis—by a respective electric motor 10, and isdefined by an abrasive face surface 12, in this case, perpendicular toaxis 9 and parallel to surface 3. Motor 10 is located outside chamber 8and is supported, together with grinding wheel 7, by a respective slide13, which is fitted movably to frame 5 and is moved, with respect toframe 5 and in a direction 15 parallel to axis 9, by a respective,conveniently step-type, motor 16 fitted in known manner to frame 5 andconnected to slide 13 by a known screw-nut screw assembly 17 (notdescribed in detail) to move respective grinding wheel 7 to and fromsupporting device 4 under the control of a central control unit 18comprising a memory 19 for storing a number of values, eachcorresponding to a reference or zero axial position of slide 13.

[0015] Still with reference to FIG. 1, motor 16, assembly 17 and slide13 form part of a positioning and adjusting assembly 20 for regulatingthe position of grinding wheel 7 in direction 15 as a function of thewear of grinding wheel 7.

[0016] Each assembly 20 also comprises an adjustable detecting device 21in turn comprising a fastening frame 22 connected integrally to frame 5of machine 1 on one side, and supporting, on the other side, a tubularbody 23 having an axis 24 parallel to axis 9, and connected integrallyto frame 22 to the side of respective grinding head 6. Each device 21comprises a rod 25, which has an intermediate portion 26 extendinginside tubular body 23, and is connected to tubular body 23 inaxially-sliding, angularly-fixed manner. Each rod 25 also comprises twoopposite lateral portions 27 and 28. Portion 27 projects frontwards onthe same side as and alongside grinding wheel 7, projects inside chamber8 and beyond the plane of abrasive surface 12 of grinding wheel 7, andterminates with an eccentric plate 30. Plate 30 extends partly facingabrasive surface 12, and is defined by a flat surface 31 extending, inthis case, over sheet 2, facing and parallel to surface 12, andwithdrawn with respect to surface 3.

[0017] Portion 28 projects from tubular body 23 on the same side asmotor 10 and inside a cup-shaped body 33 coaxial with axis 24 andcomprising a cylindrical lateral wall 34 defining an extension oftubular body 23, and an end wall 35 having an inner shoulder 36 (FIG.2). A supporting body 37 is located between shoulder 36 and the end ofportion 28, is connected integrally to portion 28, and projects radiallybeyond portion 28 to define a support for one end of a forcing spring 39surrounding portion 28, and the opposite end of which rests on aretaining ring 40 engaged in sliding manner by rod 25 and grippedbetween tubular body 23 and lateral wall 34 of cup-shaped body 33.

[0018] Still with reference to FIG. 2, device 21 also comprises a screw42 coaxial with axis 24, the head of which projects outside cup-shapedbody 33, and the threaded shank 43 of which engages a threaded hole inend wall 35, and rests against supporting body 37 to keep supportingbody 37 and plate 30 in a given axial reference position.

[0019] Device 21 also comprises an angular stop screw 44, the shank ofwhich engages a threaded hole in supporting body 37 and projectsoutwards of cup-shaped body 33 through an axial slot 45 which it engagesin axially sliding manner.

[0020] With reference to FIG. 1 and, particularly FIG. 2, device 21 alsocomprises a switch 47, which is fitted integrally to a lateral wall ofthe tubular body, is connected electrically to central control unit 18,and has a switching member 48 on which acts an arm 49 connectedintegrally to portion 27 of rod 25 and extending perpendicularly to rod25.

[0021] Operation of machine 1 and adjustment of the axial position ofgrinding wheel 7 as a function of the wear of grinding wheel 7 will nowbe described as of an ideal grinding condition, in which abrasivesurface 12 of grinding wheel 7 is in an ideal work position such as toobtain a sheet 2 of desired shape, size and surface finish; screw 42 isset to keep member 48 of switch 47 pressed in a standby condition, andto keep surface 31 of plate 30 positioned over sheet 2 and at apredetermined distance A—conveniently of a few millimeters—from surfaces3 and 12; and a zero value corresponding to the position of slide 13 andto said predetermined distance A is memorized in central control unit18.

[0022] As of the above condition, and after a predetermined or randomoperating time of grinding wheel 7, the sheet 2, if any, on device 4 isremoved; the grinding wheel is stopped; and central control unit 18transmits a control signal to motor 16 to feed slide 13 forward so thatabrasive surface 12 contacts surface 31 of plate 30. On contacting plate30, grinding wheel 7 pushes plate 30 to overcome the action of spring 39and feed rod 25 forward with respect to frame 5 to detach arm 49 fromswitch 47, which supplies central control unit 18 with a shift-startsignal. In response to the incoming shift-start signal, central controlunit 18 emits a control signal which first stops and then reverses motor16 to back up grinding wheel 7 by an adjustment quantity equal to saidpredetermined distance A, so that abrasive surface 12 of grinding wheel7 is restored to the ideal work position to obtain the desiredcharacteristics of the next sheet 2.

[0023] To compensate for any slack in the linkage mechanism, grindingwheel 7 is conveniently backed up by an adjustment quantity greater thansaid predetermined distance A, and, once the grinding wheel is backedup, central control unit 18 again reverses motor 16 and feeds grindingwheel 7 forward by the difference between said adjustment quantity andpredetermined distance A.

[0024] By backing up and, if necessary, feeding grinding wheel 7 furtherforward, the abrasive surface 12 of grinding wheel 7 is thereforerestored at all times to the ideal work position, regardless of the wearof grinding wheel 7, so that, by selecting the best frequency with whichto reposition grinding wheel 7, all the sheets coming off the machineare the same shape and size.

[0025] Using rod 25 and respective plate 30, switch 47 and all theelectric components of device 21 in general may be located away fromgrinding wheel 7 and outside chamber 8 containing the cutting fluid,thus eliminating any hazards posed by the electric components andrelative wiring coming into contact with the cutting fluid.

[0026] By providing each grinding wheel on the machine with a respectiverepositioning device, the grinding wheels can be controlledindependently, in use, which is extremely useful when, for any reason,only one or some of the grinding wheels on the machine need adjusting orreplacing.

[0027] Clearly, changes may be made to machine 1 in general, and toassembly 20 in particular, as described herein, without, however,departing from the scope of the present invention.

[0028] In particular, devices other than the one described may beprovided to move grinding wheel 7, and devices other than device 21 maybe provided to detect the instant surfaces 12 and 31 contact, and socontrol motor 16. Reference surface 31 may, obviously, be of any shapeand size, and may be selected, for example, as a function of thegeometry of the abrasive surface of the grinding wheel, which may, forexample, be lateral and concave, as opposed to a flat face surface. Inparticular, plate 30 may, obviously, be replaced with a straightforwardcylindrical rod, or a rod of any shape, positioned transversely so thatthe lateral surface of the rod cooperates with the abrasive surface ofthe grinding wheel, or frontally so that the end surface of therod—which may, obviously, be the same or a different shape and size fromthe cross section of the rod—cooperates with the abrasive surface of thegrinding wheel. In the case of a rod with a polygonal cross section, onelongitudinal edge of the rod, and therefore substantially a line, isobviously sufficient to define a reference for the abrasive surface ofthe grinding wheel.

[0029] The reference surface may therefore be a surface other than theone described, and, in particular, a luminous surface, conveniently onedefining a light beam. In which case, the instant of contact between theabrasive surface of the grinding wheel and the reference surface may bedetermined by detecting the variation in one or more characteristics ofthe light beam.

[0030] In the case of two or more side by side grinding wheels, therespective bodies/reference beams for the respective surfaces of thegrinding wheels may obviously be replaced with a single body/referencebeam common to all the respective devices 21 of the grinding wheels.

[0031] Finally, arm 49 and switch 47 may be replaced with other, e.g.optical or magnetic, devices.

1) A method of taking up wear of a grinding wheel (7) on a machine (1)for grinding sheets (2) of glass; the method comprising the steps ofsetting an abrasive surface (12) of the grinding wheel to an ideal workposition, such as to obtain a sheet of desired characteristics; andadjusting the position of the grinding wheel (7) to restore saidabrasive surface (12) to said ideal work position following wear of thegrinding wheel (7); characterized in that adjustment of the position ofthe grinding wheel (7) comprises the steps of moving said abrasivesurface (12) towards reference means (31) on said machine (1),positioned facing and a predetermined distance (A) from said abrasivesurface (12) when the abrasive surface (12) is in said ideal workposition; determining the instant of interference between said abrasivesurface (12) and said reference means (31); arresting said grindingwheel (7) at said instant of interference; and moving said abrasivesurface (12) away from said reference means (31) to an adjustmentdistance at least equal to said predetermined distance (A). 2) A methodas claimed in claim 1, characterized in that said adjustment distance isgreater than said predetermined distance (A); and by comprising thefurther step of moving said abrasive surface (12) towards said referencemeans (31) by a quantity equal to the difference between said adjustmentdistance and said predetermined distance (A). 3) A method as claimed inclaim 1, characterized in that the instant of interference is determinedby detecting a shift-start condition of said reference means (31) withrespect to a frame (5) of the machine (1). 4) A method as claimed inclaim 3, characterized in that the instant of interference is determinedby elastically locking said reference means (31) with respect to theframe (5) of the machine (1). 5) A method as claimed in claim 3,characterized in that the shift-start condition of said reference means(31) is detected by detecting a variation in a shift signal. 6) A methodas claimed in claim 5, characterized in that the shift-start conditionof said reference means (31) is detected by detecting a variation in anelectric signal emitted by an electric detector (47) connected to saidreference means (31). 7) A machine (1) for working sheets (2) of glass,comprising a supporting frame (5); a grinding wheel (7) defined by anabrasive surface (12); actuating means (16, 17) for setting andmaintaining said abrasive surface (12) in an ideal work position such asto obtain a sheet of desired characteristics; and adjusting means (20)for adjusting the position of the grinding wheel (7) with respect tosaid supporting frame (5), and restoring said abrasive surface (12) tosaid ideal work position following wear of the grinding wheel (7);characterized in that said adjusting means (20) comprise reference means(31) fitted to said supporting frame (5) and facing and a predetermineddistance (A) from said abrasive surface (12) when the abrasive surface(12) is in said ideal work position; first actuating means (16, 17, 18)for moving said abrasive surface (12) towards said reference means (31);detecting means (21) for determining the instant of interference betweensaid abrasive surface (12) and said reference means (31); stop means(16, 17, 18) for arresting said grinding wheel at the instant ofinterference; and second actuating means (16, 17, 18) for moving saidabrasive surface (12) away from said reference means (31) and to anadjustment distance at least equal to said predetermined distance (A).8) A machine as claimed in claim 7, characterized in that said first andsaid second actuating means comprise a single drive motor (16), and arespective slide (13) supporting said grinding wheel (7). 9) A machineas claimed in claim 7, characterized in that said reference meanscomprise a reference surface (31). 10) A machine as claimed in claim 9,characterized in that said reference surface (31) is parallel to saidabrasive surface (12). 11) A machine as claimed in claim 7,characterized in that said reference means (31) comprise a referenceline. 12) A machine as claimed in claim 7, characterized by comprisingrelatively movable means (23, 25, 39) interposed between said supportingframe (5) and said reference means (31); and in that said detectingmeans (21) comprise sensor means (47) for detecting movement of saidreference means (31) with respect to said supporting frame (5). 13) Amachine as claimed in claim 12, characterized in that said sensor meanscomprises an electric switch (47); connecting means (25, 49) beingprovided to connect said electric switch (47) to said reference means(31). 14) A machine as claimed in claim 13, characterized by comprisingelastic forcing means (39) for locking said reference means (31)elastically with respect to said supporting frame (5). 15) A machine asclaimed in claim 14, characterized in that said relatively movable meansand said connecting means comprise a rod (25) fitted to said supportingframe (5) to slide in a longitudinal direction (15); said elastic means(39) forcing said rod (25) against a stop (42) carried by saidsupporting frame (5). 16) A machine as claimed in claim 15,characterized in that said rod (25) extends to the side of said grindingwheel (7); said reference means (31) projecting from an end portion ofsaid rod (25); and said sensor means(47) extending on the opposite sideof said grinding wheel (7) to said reference means (31), and at adistance from the grinding wheel (7). 17) A machine as claimed in claim16, characterized by comprising adjusting means (25, 42) for adjustingthe position of said reference means (31) with respect to saidsupporting frame (5).